SOHO IMAGES COMET HYAKUTAKE'S CLOSE ENCOUNTER WITH THE SUN

NASA, the European Space Agency (ESA) and the Naval
Research Laboratory (NRL) have released a set of unprecedented
images representing a time lapse movie of Comet Hyakutake
making its close approach to the Sun.

The observations were made during April 29 - May 6,
1996 with the NRL-built Large Angle Spectrometric Coronagraph
(LASCO) instrument on the Solar and Heliospheric Observatory
(SOHO) spacecraft. The comet, estimated to have an orbital
period of 10,000 years, came within about 20 million miles of
the Sun and is seen in the images against the background of the
million-degree hot outer atmosphere of the Sun, the corona.

"Such observations require a special instrument in
space to suppress the glare of the Sun and reveal the comet and
its tails," said Dr. Guenter Brueckner, NRL's principal
investigator for LASCO. Scattering of sunlight in the Earth's
atmosphere prevented good views from the ground during the
comet's "perihelion passage," when it was closest to the Sun.

When the comet enters the outer atmosphere of the Sun,
it begins to react with the Sun's environment and can be used
as a "probe" of the solar corona. The LASCO images show the
head of the comet, and clearly visible are three separate tails
that behave differently as Hyakutake swings around the Sun.
These tails are made of different materials which react
differently with their environment. Heavy particles follow the
comet in its orbit without being redirected by an outside force
while the light dust particles are lining up away from the Sun
and are driven by the Sun's intensive radiation. Finally,
atomic particles are repelled from the comet by the solar wind
and presumably line up with the magnetic field of the solar
corona. The comet's tails could clearly be seen changing their
relative direction over the seven day observation period as the
Sun's forces acted upon them.

Hyakutake's orbit carries it back into the so-called "Oort
Cloud," a vast collection of billions of comets that is located
1.4 light years away from the solar system.

Coronal mass ejections also were observed by LASCO, in
which hot gases were expelled and accelerated by the corona's
magnetic field to travel through the interplanetary medium. A
strong reaction between such a solar high-speed cloud and the
portion of the comet's tails made of atomic particles are
expected when Hyakutake crosses the equatorial plane of the
Sun. The comet was out of LASCO's field-of-view during this
crossing, but the scientists will have another opportunity when
Hyakutake reappears from behind the Sun and can be seen later
in the southern hemisphere's night sky with ordinary
telescopes. Researchers expect to learn more about the tails
of the comet and the surrounding solar corona with more
detailed analysis.

LASCO is a joint project between NRL, the Max Planck
Institut fur Aeronomie (Germany), the Laboratoire d'Astronomie
Spatiale (France), and the School of Physics and Space Research
at the University of Birmingham (UK). SOHO is a project of
international cooperation between ESA and NASA.

More information can be found on the LASCO Comet
Hyakutake page on the World Wide Web at URL: